Conversion of alkyl aromatics



United States Patent ()fihce 3,304,339 Patented Feb. 14, 1967 3,304,339 CONVERSION OF ALKYL AROMATICS Hans A. Benesi, Berkeley, Calif., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Feb. 25, 1966, Ser. No. 529,949 6 Claims. (Cl. 260668) This application is a. continuation-in-part of application Serial No. 318,833, filed October 25, 1963, now abandoned.

This invention relates to a process for the catalytic conversion of alkyl aromatic hydrocarbons and relates more particularly to a process for the isomerization of xylenes.

The catalytic isomerization of xylenes and similar low molecular weight alkyl benzenes is known. For example, aluminum chloride promoted with hydrogen chloride was a very early catalyst suggested for this isomerization reaction. Subsequently, other catalysts such as a Group VIII metal supported on a refractory oxide support have been proposed for the isomerization of xylenes. See, for example, U.S. Patent 2,976,332 to Leurn et al.

In general, previously suggested catalysts have a disadvantage such as one or more of the following: (1) the catalyst is expensive, (2) the catalyst is insufficiently active to be used in a commercial process, (3) the catalyst is sufliciently active, but ultimate life is too short to be of commercial interest, or (4) the catalyst has oor selectivity for the isomerization reaction, i.e., the catalyst promotes side reactions such as cracking and hydrogenation which produce coke and gases and/or reduce the yield of isomerized aromatics.

It has now been found that alkyl aromatices such as xylenes'can be isomerized at an elevated temperature by means of a catalyst comprising silver and fluoride composited with acid-acting refractory oxide cracking catalyst. In accordance with one embodiment of the invention, xylene is contacted with a catalyst comprising silver and fluoride composited with silica-alumina in the presence of hydrogen at a temperature in the range from about 400 to 900 F. The silver catalyst is more highly active than a similar catalystcomprising, for example, copper.

The predominant portion of the catalyst is an acidacting refractory oxide which is generally referred to as the base for the catalyst. A strongly acidic base such as silica-alumina comprising about 60 to 90% by weight silica gives excellent results. Silica-alumina is generally known as primarily an amorphous material and is to be distinguished from the crystalline alumino-silicates such as faujasite and mordenite. Silica-alumina and its preparation is well known in the art. (See chapter 1 by Ryland et al. in Cataysis VII, Emmett, 1960, Reinhold Publishing Co.) If desired, other cracking catalysts such as silica-alumina-magnesia, silica-titania, silica-titania zirconia and the like may be used. In certain cases, alumnia, rendered acidic by the addition of halogen or aluminaboria may be used.

The silver and the fluoride can be composited with the siliceous cracking base in any suitable manner, such as by impregnation, ion-exchange, or the like. The amount of silver in the catalyst can vary over a broad range and is from about 0.1 to 20% by weight, expressed as elemental metal. Preferably, the amount of silver is in the range from about 1 to 10% by weight. The amount of fluoride in the catalyst is in the range from about 0.1 to 5% and preferably from about 1 to 4% by weight. A highly active and suitable catalyst contains about 3 to 8% w. silver, and about 1 to 3 w. fluoride on a silica-alumina cracking catalyst base of about 10-30% w. alumina, the silver being ion-exchanged into the base.

Feed to the process of the invention can be a substantially pure xylene isomer, a mixture of xylene isomers, or a hydrocarbon fraction rich in xylene isomers. For example, a source of xylene isomers is the C aromatic fraction recovered from catalytic reformates or coal tars. The xylene fraction remaining after separating and recovering all or a part of a given isomer from such a source is a suitable feed for the process of the invention. Thus, para-xylene, which is of growing importance, can be recovered from a C catalytic reformate fraction by low temperature crystallization. The mother liquor produced from such low temperature crystallization is deficient in para-xylene with respect to the thermodynamic equilibrium concentration of xylene isomers and is an excellent feed to the present process. Moreover, catalytic reformates contain appreciable quantities of ethylbenzene which is difficult to remove from the xylene. In the present process, the ethylbenzene undergoes appreciable conversion to other hydrocarbons, especially disproportionation products, which can be removed. This is advantageous for on separation of the C product into one or more xylene isomers, e.g., by crystallization, and return of the residue C hydrocarbons, there is less tendency for a buildup of ethylbenzene in the system.

The process of the invention is carried out at a temperature in the range from about 400 to 900 F. and preferably from about 482 to 752 F. In general, higher conversions are obtained as temperature is increased.

The isomerization reaction can be conducted over a wide range of space velocities, such as a space velocity in the range from about 0.5 to 25, but is preferably at a space velocity in the range from about 1 to 10. In general, conversion decreases with an increase in space velocity, although selectivity is generally increased. Space velocity, as the term is used herein, refers to WHSV and is expressed as weight of feed per hour per unit weight of catalyst.

The isomerization reaction is carried out in the presence of hydrogen; however, there is little or no net consumption of hydrogen in the process. Any consumption of hydrogen is the result of side reactions, such as hydrogenation of the aromatics and it is preferred to keep such reactions to a minimum. The presence of hydrogen functions to improve catalyst life, apparently by preventing polymerization of intermediate reaction products which would otherwise polymerize and deposit on the catalyst. Hydrogen apparently also functions to improve conversion and selectivity for the isomerization reaction. A hydrggen to hydrocarbon mole ratio of from about 1:1 to 25:1 or higher and preferably from about 5:1 to 15:1 is used. It is not necessary to employ pure hydrogen, since hydrogen-containing gases, e.g., hydrogen-rich gas from the catalytic reforming of naphthas, are suitable. Total pressure can be in the range from about atmospheric to about 1500 p.s.i.g. and preferably from about 10 0 to 1000 p.s.i. For a given space velocity, as pressure is increased, actual residence time is increased which tends to increase conversion.

In the present process, as in any known xylene isomerization process, the reaction zone efiiuent contains a mixture of the three xylene isomers even when the feed is a. single isomer or a mixture of two isomers. To obtain a specific xylene isomer, the isomerizationproduct is recovered and subjected to a suitable separation such as the use of low temperature crystallization, the use of complexing agents, and the like. Such separation processes are well known and as they are not a part of the isomerization process of the invention, a description of separation methods is unnecessary.

Example 1 Silica-alumina powder (American Cyanamid MS-A-3 cracking catalyst of approximately 25% w. alumina) was formed into granules and composited with silver and 4 F. (350 C.), 1000 p.s.i.g., 26/1 H /oil mole ratio, and 8 WHSV. Conversion of o-xylene was only 25.9% w., even at the somewhat higher temperature, with the product containing 24.2% W. mand p-xylene.

and fluorine. The granules were contacted with an am- 5 Exam I IV moniacal solution of NH HF and AgNO followed by p g drylgg and calcmmg 2 (550 g for The silver catalyst of Example I was tested for the conig T e final catalyst Contained g and version of a C mixture containing 20.1% ethylbenzene fi g y was tested for the iomerization of o 10 and 79.6% W. o-xylene. The conversion was carried out s n a Q at 572 F. 00 C. 1000 .s.1. 26/1 H /o1l ole ratio xylene at 572 F. 300 0. 1000 p.S.1.g., 26/1 H /o1l and 8 SQ, P 2 m 5 i 8 (lwelght hourly space Veloclty) For comparison, a silver catalyst having a crystalline esu ts are given m a e alumino-silicate as the support was tested under the same TABLE I conditions. The catalyst was prepared from the sodium Conversion, percent w. 61.8 form of mordenite (Zeolon from the Norton Co.) which Products, percent w.: was first washed with ammonium nitrate to replace sodium C paraffins 0,2 ions with ammonium ions. Silver ions from a silver Benzene 0,4 nitrate solution were then exchanged into the ammonium Toluene 5,1 mordenite, and the catalyst was washed, dried, and o-Xylene 38,2 calcined at l022 F. (550 C.). The final catalyst conm-Xylene-p-xylene 50,1 tained 4.7% w. Ag. Trimethylbenzenes 6.0 Results of the tests are given in Table III, catalyst A Tetramethylbenzenes 0.1 and B being the silica-alumina and mordenite catalyst,

Example H respectively.

A series of catalysts were prepared using the silica- T ABLE HI alumina powder of Example I as a support. The s1l1ca alumina was contacted with an ammoniacal solution of ammonium bifiuoride and metal [Ag+, Ni++, and l A I B Pt(NH in the form of nitrates (except for the platinum where the chloride was used), followed by washing, YE conversiom Percent drying at 248 F. (120 0. and calcining in air at 1022 3 Zj2ci?' 3 5 F. (550 C.) for 16 hours. 23323 $3 8-; The various catalysts were tested for the isomerization 35 ToinensIIIIIII n 'I 714 ols of o-xylene at 572 F. (300 C.), 1000 -p.s.i.g., 26/1 g-lg g gg 25g 52-: H oil mole ratio, and 8 WHSV, except for silicag;i;,1g alumina alone which was tested at 4 WHSV. Results Ctand clt'alkylbenzeues are given in Table 11.

TABLE II 2.5% w. F 10.1% w. Ag 5.0% 0.4% Pt, silicaralumuia Silica-alumina Silicaelumina Ni/0.2% F 03% w. F

Silica-alumina Silicaralumina Conversion, percent w 6. 2 6. 2 12. 4 100 100 Products, percent w.:

0 paraflius. 0.1 0. 1 0. 1 Benzene"- 0.1 0. 2 0. 2 Toluene" 0. 2 0. 2 0. 2 o-Xylene 0s. 8 93. s 86. 6 rn-Xylenep-xylene 5. 3 5. 5 11. 6 Trirnethylbenzenes 0. 3 0.3 0. 2 Tetramethylbemenes.-- O. 2 0. 0 0. 1 Hydrogenated C s 0.0 0.0 0.0

From the above results it can be seen that little isomer- From the above results, the high conversion of both ization of o-xylene is efiected under these conditions. xylene and ethylbenzene are obtained with silver on fluo- Nickel or platinum (which have strong hydrogenation acrided silica-alumina. tivity) on fluorided silica-alumina is not selective for I claim as my invention: isomerization at these conditlons as the o-xylene is com- 1. A-process f isomerizing axylene isomer hi h p y Y rather than lsomeflled- It Should prises contacting said isomer in the presence of hydrogen be noted that plat num catalysts are more advantageously in an isomerization zone at a temperature in the range employed 213 l gf c s 6: from about 200 to 500 C. with a catalyst comprising a cut an silver and fluoride composited with an acid-acting crack- WhlCh favors a low equilibrium concentration of naphinc catalyst thenes. However, under such conditions, undesirable side Th e process according to claim 1 wherein the catalyst reactions are usually encountered.

comprises from about 0.1% to 20% by weight silver and 7 Ex p III I frorgi albout 10.1% to 5% by Weight fluoride composited A copper catalyst containing 7.5% w. Cu 'and 0.3% Wlt S1 lea-a w. F was prepared with the silica-alumina cracking cata- T p ce a rding to claim 1 wherein the isomerlyst in the manner described in lixample II. This cataization is carried out at a pressure in the range from about lyst was tested for the isomerizatron of o-xylene at 662 atmospheric to about 1500 pounds per square inch.-

4. The process according to claim 1 wherein the xylene isomer is in admixture with ethylbenzene and a C fraction comprising xylenes and ethylbenzenes is recovered from the efliuent from the isomerization zone.

5. The process according to claim 4 wherein a xylene isomer is separated from the C fraction and remaining C hydrocarbons are recycled to the isomerization zone.

6. The process according to claim 5 wherein the catalyst comprises from about 0.1% to 20% by weight silver and about 0.1% to 5% by weight fluoride composited with silica-alumina.

References Cited by the Examiner FOREIGN PATENTS 744,467 2/1956 Great Britain.

DELBERT E. GANTZ, Primary Examiner.

C. R. DAVIS, Assistant Examiner. 

1. A PROCESS FOR ISOMERIZING A XYLENE ISOMER WHICH COMPRISES CONTACTING SAID ISOMER IN THE PRESENCE OF HYDROGEN IN AN ISOMERIZATION ZONE AT A TEMPERATURE IN THE RANGE FROM ABUT 200 TO 500*C. WITH A CATALYST COMPRISING SILVER AND FLUORIDE COMPOSITED WITH AN ACID-ACTING CRACKING CATALYST. 